Re: [Qemu-devel] [PATCH v3 02/14] doc: update AMD SEV to include Live migration flow

[Dr. David Alan Gilbert]

* Singh, Brijesh (address@hidden) wrote:
> Signed-off-by: Brijesh Singh <address@hidden>

Reviewed-by: Dr. David Alan Gilbert <address@hidden>

> ---
>  docs/amd-memory-encryption.txt | 40 +++++++++++++++++++++++++++++++++-
>  1 file changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/amd-memory-encryption.txt b/docs/amd-memory-encryption.txt
> index 8822cadda1..01d95089a8 100644
> --- a/docs/amd-memory-encryption.txt
> +++ b/docs/amd-memory-encryption.txt
> @@ -89,7 +89,45 @@ TODO
>  
>  Live Migration
>  ----------------
> -TODO
> +AMD SEV encrypts the memory of VMs and because a different key is used
> +in each VM, the hypervisor will be unable to simply copy the
> +ciphertext from one VM to another to migrate the VM. Instead the AMD SEV Key
> +Management API provides sets of function which the hypervisor can use
> +to package a guest page for migration, while maintaining the confidentiality
> +provided by AMD SEV.
> +
> +SEV guest VMs have the concept of private and shared memory. The private
> +memory is encrypted with the guest-specific key, while shared memory may
> +be encrypted with the hypervisor key. The migration APIs provided by the
> +SEV API spec should be used for migrating the private pages. The
> +KVM_GET_PAGE_ENC_BITMAP ioctl can be used to get the guest page encryption
> +bitmap. The bitmap can be used to check if the given guest page is
> +private or shared.
> +
> +Before initiating the migration, we need to know the targets machine's public
> +Diffie-Hellman key (PDH) and certificate chain. It can be retrieved
> +with the 'query-sev-capabilities' QMP command or using the sev-tool. The
> +migrate-set-parameter can be used to pass the target machine's PDH and
> +certificate chain.
> +
> +During the migration flow, the SEND_START is called on the source hypervisor
> +to create an outgoing encryption context. The SEV guest policy dictates 
> whether
> +the certificate passed through the migrate-sev-set-info command will be
> +validated. SEND_UPDATE_DATA is called to encrypt the guest private pages.
> +After migration is completed, SEND_FINISH is called to destroy the encryption
> +context and make the VM non-runnable to protect it against cloning.
> +
> +On the target machine, RECEIVE_START is called first to create an
> +incoming encryption context. The RECEIVE_UPDATE_DATA is called to copy
> +the received encrypted page into guest memory. After migration has
> +completed, RECEIVE_FINISH is called to make the VM runnable.
> +
> +For more information about the migration see SEV API Appendix A
> +Usage flow (Live migration section).
> +
> +NOTE:
> +To protect against the memory clone SEV APIs are designed to make the VM
> +unrunnable in case of the migration failure.
>  
>  References
>  -----------------
> -- 
> 2.17.1
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK